1. Field of the Invention
The present application relates generally to nucleic acid systems for triggering RNAi for modulating the expression of one or more marker genes in the presence of a detection target.
2. Description of the Related Art
RNA interference (RNAi) is a conserved biological response to double-stranded RNA (dsRNA) that results in sequence-specific silencing of target gene expression (Fire et al. 1998 Nature 391: 806-811). In recent years, RNAi has been adopted as an important experimental tool to study and manipulate gene expression and has generated great interest as a potential therapeutic approach (Dillon et al. 2005 Annual Review of Physiology 67: 147-173, incorporated herein by reference in its entirety).
Until now, in the practice of using RNAi for gene silencing, an RNA duplex is introduced into the cell cytoplasm such that one of the strands in the duplex matches the sequence of the target mRNA to be silenced. In the traditional RNAi pathway, an “inactivator dsRNA” is introduced into the cell's cytoplasm and is processed by the Dicer enzyme, producing small interfering RNAs (siRNAs). (See, Tijsterman and Plasterk 2004 Cell 117(1): 1-3, incorporated herein by reference in its entirety). The siRNAs are then processed by the RNA-induced silencing complex (RISC complex), which unwinds the siRNA and retains one strand as a targeting co-factor. The RISC-siRNA complex recognizes and induces the degradation of the target mRNA, which is complementary to the siRNA strand retained by the RISC complex. The cleaved mRNA is then further degraded by natural mechanisms. The traditional RNAi mechanism implements the logical operation: if gene q is detected, silence gene q. Thus, using the standard RNAi technique, the detection and silencing steps are restricted to operating on the same gene.